Optical navigation systems detect relative movements between the optical navigation systems and target or navigation surfaces to perform tracking operations. An optical navigation system uses a light source, such as a light-emitting diode or a laser diode, to provide illumination light on a navigation surface and an image sensor to successively capture frames of image data in response to the illumination light reflected off the navigation surface. The optical navigation system compares the successive frames of image data and estimates the relative movements between the optical navigation system and the navigation surface based on the comparison between the current frame of image data and a previous frame of image data. The optical navigation system is able to track the relative movements between the optical navigation system and the navigation surface by continuously capturing and comparing frames of image data.
Optical navigation systems are commonly used in optical computer mice to track the lateral movements of the mice relative to the navigation surfaces on which the mice are manually manipulated. An optical computer mouse typically requires a minimum volume in order for the optical navigation system in the optical computer mouse to generate high contrast images with a large field of view (i.e., a region on the navigation surface captured by the image sensor). Image contrast is important for an optical navigation system since the noise in the system will otherwise dominate, which makes it difficult to accurately determine the displacement of the optical computer mouse relative to the navigation surface. Field of view is also important for an optical navigation system to capture large frames of image data in order to measure high velocity movements (e.g., 20 to 30 inches per second).
While some navigation surfaces readily produce high contrast frames of image data, other navigation surfaces such as surfaces of glass tables, i.e., surfaces of sheets of glass on tabletops or glass tables with no structure directly under the field of view, do not when probed by conventional optical mice. Furthermore, the field of view usually scales with the focal length of the optical navigation system, and consequently, the height of the system. Thus, it is desirable to have an optical navigation system that can produce frames of image data with high contrast and a large field of view for a wide variety of surfaces, including glass tables, in a small a volume as possible.